This invention relates to an improved construction of a rotary hearth such as used in calcining kiln.
As is known in the prior art, limestone, which is largely calcium carbonate, is reduced to lime or calcium oxide by subjecting the limestone to high heat for a predetermined period of time. In one method of calcining, shown for example in U.S. Pat. No. 3,345,052, issued to Hubert L. Hall, limestone is deposited in the form of small pellets on the surface of an annular hearth which is rotated continuously on a vertical axis to carry the pellets through successive heating zones of an annular kiln. After the pellet material has been reduced to lime and at a certain point along the circular course, a belt or the like with vanes or pushers sweeps the lime outwardly onto a stationary chute down which the lime slides into a hopper or the like.
In kiln assemblies of the prior art, the rotating hearths have used steel plate, castings or a combination of both to retain the refractory material. While this type of construction provides peripheral containment of the refractory material, unequal expansion of metal and refractory portions of the hearth due to heat often results in cracking of the refractory material and jamming of the hearth.